Suction pump

ABSTRACT

A medical suction pump including a pump housing having a filament therein which is alternately heated and cooled by passing electric current therethrough in response to the operation of a thermostatically controlled switch which is alternately heated and cooled by a resistance element, an inlet conduit in communication with the pump which communicates suction pressure produced by the pump to a patient during the cooling of gases within the housing, the parameters of the electrical circuit being such as to always heat the filament sufficiently so as to cause the pump to always be capable of producing a suction pressure in excess of predetermined value regardless of the variable conditions to which the pump is subjected, and a control valve assembly in the suction line responsive to the suction pressure created by the pump to selectively bleed a variable amount of air into the inlet conduit to maintain the suction pressure at said predetermined value.

United States Patent [72] inventor Staniord'A. Henderson 49 Wansfell Road, Snyder, N.Y. 14226 [21] Appl. No. 858,704 [22] Filed Sept. 17, 1969 [45] Patented Nov. 30, 1971 [54] SUCTION PUMP 11 Claims, 4 Drawing Figs.

[52] 11.8. C1 417/137, 128/276 [51] Int. Cl A61m l/00, F041 l/06, F04f 3/00 [50] Field of Search 417/137, 278,139, 149, 442, 458, 506, 566; 128/276, 277, 278

[56] References Cited UNITED STATES PATENTS 1,755,318 4/1930 Dinesen 128/276 2,346,841 4/1944 Henderson 417/137 Primary ExaminerCarlton R. Croyle Assistant Examiner-Richard E. Gluck AttorneySommer, Weber & Gastel ABSTRACT: A medical suction pump including a pump housing having a filament therein which is alternately heated and cooled by passing electric current therethrough in response to the operation of a thermostatically controlled switch which is alternately heated and cooled by a resistance element, an inlet conduit in communication with the pump which communicates suction pressure produced by the pump to a patient during the cooling of gases within the housing, the parameters of the electrical circuit being such as to always heat the filament sufficiently so as to cause the pump to always be capable of producing a suction pressure in excess of predetermined value regardless of the variable conditions to which the pump is subjected, and a control valve assembly in the suction line responsive to the suction pressure created by the pump to selectively bleed a variable amount of air into the inlet conduit to maintain the suction pressure at said predetermined value.

PATENTEUuuv 30 Ian 3, 624.82 1

INVENTOR.

ATTOR/VFY SUCTION PUMP The present invention relates to an improved medical suction pump which is especially constructed for removing liquids or gases from patients.

By way of background. a medical suction pump. such as shown in U.S. Pat. No. 2,346,841, is used to drain fluids from body cavities. This pump operates by cyclically heating air in a pump chamber. When the air is heated, it expands, and a part of it is forced from the chamber. When the remaining air in the pump chamber cools, a partial vacuum is created. and this partial vacuum is communicated to a catheter which is inserted in an area to be drained. The partial vacuum causes fluids to be drawn into the catheter and to be deposited in a fluid trap. By the alternate heating and cooling of the gases in the pump chamber, a gentle intermittent pumping action is obtained, thus causing excess liquids to be removed from a persons body during the cooling of gas within the pump chamber and permitting fluid to accumulate in the area being drained while the pump chamber is heated. The accumulation of fluids permits the body tissues to be periodically immersed in the liquids which are so necessary to their sustained functioning. it is with an improvement in the foregoing type of medical suction pump that the present invention is concerned.

Pumps of the foregoing type were subject to the shortcoming that a number of factors caused both their suction pressure and pumping capacity to fluctuate. This was undesirable because it caused a great amount of uncertainty as to the amount of drainage, frequency of drainage, and amount of suction pressure to which a patient's organs were subjected. More specifically, the air within the pump chamber was cyclically heated by a resistance heating element. However, the degree of heating varied directly with the line voltage. As the line voltage decreased, both the pumping capacity and the suction pressure decreased accordingly because the filament was heated to a lower temperature. Furthermore, the heating and cooling cycles varied with the ambient temperature. More specifically, the length of the heating cycle was controlled by a thermal relay. If this relay was located in a cool area, such as next to an open window, a longer heating time was experienced which in turn produced a longer heating cycle and a shorter cooling cycle for the heating filament in the pump chamber. This in turn generally resulted in a higher suction pressure than for which the equipment was set. The opposite result was generally experienced if the thermal relay, which controlled the length of the heating cycle, was placed in an area where the ambient temperature was high, as next to a radiator. In this case the heating cycle was shortened with attendant decreases in both the displacement volume and suction pressure. Thus, there was no reasonable certainty that the patient would be provided with the quantitative suction therapy desired by the physician. It is with the overcoming of the foregoing deficiencies of the prior art suction pumps that the present invention is concerned.

lt is accordingly the primary object of the present invention to provide an improved medical suction pump in which the desired suction pressure is accurately controlled, thereby always subjecting the organ being drained to a predetermined constant suction pressure.

Another object of the present invention is to provide an improved medical suction pump in which the displacement volume is maintained relatively constant during all cycles of operation regardless of the ambient temperature and other variables to which the pump is subjected.

A further object of the present invention is to provide an improved medical suction pump which includes a highly simplified electrical control circuit, thereby reducing the possibility of electrical malfunction. Other objects and attendant advantages of the present invention will readily be perceived hereafter.

The improved suction pump of the present invention basically includes a pump housing having a filament therein which is alternately heated and cooled by passing electric current therethrough in response to the operation of a thermostatically controlled switch which is alternately heated and cooled by a resistance heating element. The parameters of the circuit are such that the filament in the pump housing is always heated sufficiently. even under the most adverse conditions, so as to be capable of providing a suction pressure, during the cooling cycle of the pump, which is always in excess of the maximum predetermined desired suction pressure. A control valve assembly is located in the suction line leading to the pumping chamber and whenever the suction pressure in the pump chamber exceeds a predetermined maximum, which is practically always the case for the majority of the time that suction is being produced, the control valve assembly will be actuated to bleed atmospheric air into the pump chamber at a variable rate which causes the suction pressure in said pump chamber to always be maintained at substantially the predetermined desired value. By maintaining the suction pressure substantially constant regardless of the variables which can affect it, such as variations in line voltage, variations in ambient temperature, etc., the volume of displacement of the pump is very closely regulated because the major contributing factor which controls the displacement volume of the pump is the suction pressure. Thus the pump always provides substantially constant displacement at substantially constant suction pressure. The control valve assembly preferably includes structure for producing a number of maximum pressures which can be selectively utilized.

The various aspects of the present invention will be more fully understood when the following portions of the specification are read in conjunction with the accompanying drawings wherein:

FIG. I is a diagrammatic representation of the improved suction pump of the present invention including the improved control circuit therefor and a control valve assembly for maintaining the suction pressure at a predetermined desired level;

FIG. 2 is a fragmentary enlarged view of the control valve assembly which is utilized to maintain constant suction pressure;

FIG. 3 is a diagrammatic view of a modified form of the present invention which limits the maximum suction pressure obtainable by the pump and also permits electrical control to obtain lower pressures; and

FIG. 4 is a fragmentary view of a modified form of control valve which permits adjustment of the maximum suction pressure.

The improved pump 10 of the present invention includes a conduit 11 which has one end mounting a catheter (not shown) which is inserted in an area to be drained. The opposite end of conduit 11 is mounted on conduit 12 which passes through stopper 13 mounted in the opening of suction bottle 14 which receives wastes I5 from the patient. A second conduit 16 also extends through stopper l3 and mounts conduit 17 at its upper end. By applying suction to conduit 17 periodically there is a corresponding periodic suction applied to the air located in chamber 18 above liquid 15 and this suction is communicated to the patient through conduit II. lt can readily be seen that the lower end 19 of conduit 16 is well above the liquid 15 in bottle 14 so that only gases will be withdrawn from the bottle, the liquid 15 remaining therein to be emptied as required.

The suction pump 10 includes a pump housing 20 which provides a closed chamber 21. A continuous heating filament 22 is strung about end discs 23 and 24 which are made of mica or other suitable dielectric material which supports filament 22 so that it does not touch itself or the walls of housing 20. The ends of filaments 22 extend through insulating plugs 25 and 26 which are mounted in end cap 27 secured in fluidtight relationship to housing 20.

Periodic heating and cooling of filament 22 will provide an alternate exhaust and intake of gases, respectively, from pump chamber 21, which in turn will provide an intermittent evacuation of bottle chamber 18 during the cooling cycle of filament 22. More specifically during the heating of filament 22 the air in chamber 21 will expand and will be forced through conduit 28 in communication therewith into chamber 29 of check valve housing 30. At this time ball check valve 31 will remain seated, but ball check valve 32 will be caused to unseat because of the pressure to permit the gases to pass from chamber 29 through chamber 33 and vent 34' to the atmosphere. After evacuation of chamber 21 has been completed at the end of the heating cycle and filament 22 begins to cool, any remaining gases in chamber 21 will be contract, thereby forming a partial vacuum within chamber 21 which in turn is communicated to chamber 29 of check valve housing 30 via conduit 28. This will cause ball check valve 32 to seat thereby terminating communication of chamber 29 with the atmosphere through vent 34'. However, at this time ball check valve 31 will unseat so as to place conduit 18' in communication with pump chamber 21 via conduit 34 on which conduit 18' is mounted, check valve chambers 35 and 29, and conduit 28. As filament 22 cools and the gases within chamber 21 contract, the suction or vacuum produced in chamber 21 will thus be communicated to chamber 18 of bottle 14 via conduit 18', pressure control valve assembly 17' and conduit 17. This suction, in turn, will be communicated to the catheter mounted at the end of conduit 11 and thus removes the accumulation of fluids from the patient during this portion ofthe pumping cycle.

In order to effect the foregoing alternate heating and cooling of filament 22 a control circuit is provided. This control circuit includes leads 36 and 37 which are connected to a suitable voltage source. Lead 36 is connected to an on-off switch 38, which is, in turn, connected to lead 40. Lead 40 in turn is coupled to lead 41 having a lamp 42 in series therein, with lead 41 being coupled to lead 37 via lead 43. Thus, whenever on-ofi switch 38 is in the on position, indicator lamp 42 will be ignited to show that the apparatus is operating.

The cycles of heating and cooling of element 22 are controlled by thermostatic switch 44. More specifically, a bimetallic element 45 is mounted on insulating base 46 which also mounts a normally closedmicroswitch 47. When voltage is applied across leads 36 and 37 and bimetallic element 45 is in the position shown in the drawing, there will be a flow of current through lead 36, switch 38, lead 40, lead 53, normally closed microswitch 47, lead 47, lead 50, resistance heating wire 49 which is wound around bimetallic element 45, lead 48, lead 43, and lead 37 to complete the circuit. In addition, there will be a flow of current through lead 36, switch 38, lead 40, lead 53, closed microswitch 47, lead 47', lead 51, resistance heating element 22, lead 53', and lead 37 to complete the circuit. Thus, while resistance heating element 49 is being heated chamber 21 will also be heated. The heating of resistance 49 will continue until such time as bimetallic element 45 deflects due to the heating so that the end of adjusting screw 52 engages microswitch 47, at which time switch 47 will be caused to open thereby terminating current flow to both resistance heating element 49 and filament 22. At this time resistance heating element 49 will commence to cool and screw 52 will ultimately move out of contact with microswitch 47. However, while screw 52 is in contact with microswitch 47, heating element 22 is not heated so as to permit the gases in chamber 21 to cool, to provide a suction cycle. After screw 52 loses contact with microswitch 47, the latter will close and the heating circuit will again be energized to start the heating cycle, which is then repeated. By backing screw 52 away from microswitch 47, the length of the heating cycle can be prolonged as it will take a greater amount of heating of resistance element 49 to open switch 47 In accordance with one aspect of the present invention a pressure control valve assembly 17' is provided for the purpose of closely controlling the suction pressure produced by the pump. At this point it is to be noted that the parameters of the electrical circuit are such as to always cause filament 22 to heat up sufficiently to be capable of expelling enough gases from pump chamber 21 so that when the gases cool, a suction pressure can be obtained which is greater than is actually desired. In other words, if 120 mm. of suction is desired, the pumping chamber will be capable of providing a suction pressure which is greater than 120 mm., and this in turn will result from heating filament 22 to a temperature which is greater than that required to obtain 120 mm. of suction. At this point it is also to be noted that the parameters of the electrical circuit are such as to always be capable of giving the foregoing result, even under the most adverse conditions. For example, even if the ambient temperature is high so that thermal relay 44 will produce a short heating cycle, there will be enough heat generated by filament 22 to produce sufficient evacuation of chamber 21 to provide a suction in excess of the maximum desired suction. It will be appreciated of course that if the thermal relay. 44 is in a cool ambient area, the heating cycle of filament 22 will be much longer than when it is in a high ambient area so that pump chamber 21 will be capable of producing a suction pressure which 18 even greater. At this point it is to be noted that the greatest single factor which controls the pump displacement is the suction pressure. Therefore, the close control of the suction pressure will produce a relatively constant pump displacement.

In the embodiment shown in FIG. 2, the valve assembly will provide two operating pressures, either a high suction, for example, 120 millimeters of mercury or a low suction, for example, millimeters of mercury. If it is desired to obtain the higher suction, valve 55 is manually closed to prevent the atmosphere from communicating with conduit 56. Therefore, when the gases are cooling in pump chamber 21, there will be communication between conduit 17 leading from the bottle 14 and conduit 18 leading to the pump housing 20 via fourway tee connection 57, conduit 58 and four-way tee 59. The pressure in these conduits will also be in communication with chamber 60 of high-pressure control housing 61 via conduit 61 and chamber 62 of low-pressure control housing 63 via conduit 63. The pressure in conduit 18 will also be in communication with conduit 64 of high-pressure control housing 61 via conduit 65. The pressure in conduit 18' will also be in communication with conduit 66 of low-pressure control housing 63 via conduit 67. A flexible diaphragm 68 is sandwiched between the annular edge 69 of housing 61 and housing cap 70 by means of screws 71. A spring 72, which is located between housing 61 and diaphragm 68, biases diaphragm 68 against annular seat 73 on cap 70. For the initial short period of the cooling cycle of filament 22 the pressure in conduits 17 and 18' will not exceed a predetermined maximum, for example, mm., and diaphragm 68 will remain seated on seat 73 under the bias of spring 72. However, when the pressure in conduits 17 and 18' tends to exceed the predetermined desired maximum of 120 mm., diaphragm 68 will be pulled upwardly against the bias of spring 72, and thus uncover seat 73. This occurs because the upper side of the diaphragm has a greater area exposed to the pressure. At this time air from the atmosphere will enter the vent 74 and this air will bleed into conduits 64 and 65 which are in communication with conduit 18', thereby decreasing the suction pressure in conduit 18' and consequently decreasing the suction applied to the patient. It will be appreciated, of course, that spring 72 is of a predetermined strength to give the foregoing result. The diaphragm 68 will stabilize at a location where it permits only enough air to bleed into conduit 65 to maintain the pump suction at an even l20 mm., for example, or any other desired maximum suction pressure. During the foregoing action diaphragm 75 will not be unseated from seat 79 because valve 55 remains closed.

If the pump is to be operated at a lower pressure, for example, 90 mm. of suction, valve 55 is opened to permit conduit 56 to communicate with the atmosphere. Valve housing 63 has a diaphragm 75 mounted therein which is sandwiched between an annular edge 77' of said housing and annular cap 76 which is secured to the housing by means of screws 77. A spring 78 biases diaphragm 75 against seat 79 on cap 76. Spring 78 is weaker than spring 72. Therefore, if the suction pressure in conduit 18 exceeds the predetermined maximum low pressure which is desired, the diaphragm 75 will be pulled to the left and unseated from its seat 79 to permit conduit 66 to be vented to the atmosphere through conduit 56. This will permit atmospheric air to bleed into conduit 18' via conduits 56, 66, 67 and tee 59, thereby maintaining the pressure in conduit 18' at a predetermined low maximum, because diaphragm 75 will adjust its position under the opposing influences of spring 78 and the suction in chamber 62 so as to permit the bleeding of only sufl'icient air into conduit 18 to maintain the suction constant. It will be appreciated that diaphragm 68 will not unseat during low-pressure operation because spring 72 is of greater strength than spring 78, as noted above.

By the use of the pressure control valve 17' as described above, the maximum predetermined pressure can be controlled very accurately. It will be appreciated that each of the diaphragms 68 and 75 will tend to fluctuate relative to their respective seats as the suction pressure produced by the pump varies during their respective operation. Thus as the suction pressure increases, the diaphragms will be pulled further away from their seats to permit more air from the atmosphere to be vented into the pump chamber. As the pressure decreases, the diaphragms will approach their seats and thus permit less venting to take place. It is by this fluctuating action of each of the diaphragms that the pressure is maintained relatively constant during pump operation, that is, it cannot exceed the predetermined maximum as determined by the strength of the springs.

It will be appreciated that any number of subassemblies comprising a valve housing and a spring biased diaphragm can be incorporated into the control valve assembly so as to permit the pump to provide any predetermined number of maximum pressures. To cause any desired predetermined pressure to be obtained, it is merely necessary to terminate the venting of all of the subassemblies which will provide lower pressures, in a manner analogous to that described above relative to the control valve assembly 17.

It can thus be seen that the use of the control valve assembly 17' eliminates the need for electrical controls for varying the suction pressure produced by the pump. In this respect, in the past the maximum pressure was controlled by the rate of pump heating which in turn required a variable resistance in series with filament 22. By the use of the control valve assembly of the present invention the variable resistance is not required as a predetermined current is always applied to filament 22 and the suction pressure is controlled by bleeding atmospheric air into the inlet conduit. Thus, not only is the maximum pressure produced by the pump maintained at a relatively constant level at all times but also the amount of air displacement which the pump produces up to the point of venting is also maintained relatively constant during all cyclesof operation because filament 22 is always heated substantially the same amount.

If desired, instead of utilizing a different strength spring for each desired maximum pressure as shown in the FIG. 2 embodiment, an adjustable spring can be used. This is shown in FIG. 4 wherein a screw 81 bears on plate 82 which in turn bears against spring 72' which is analogous to spring 72. The inlet to chamber 60 is through conduit 61 which is analogous to conduit 83' of FIG. 2, with conduit 83 being offset to permit the use of adjusting screw 81. By the use of an adjusting screw such as shown in FIG. 4, the maximum pressure can be adjusted to any value.

In FIG. 3 a still further alternate embodiment of the present invention is disclosed. This embodiment utilizes essentially the same circuit as shown in FIG. 1 of the drawings for electrically controlling the pumping cycle. However, this circuit includes a variable resistance 90 between leads 51 and 50. This variable resistance is used to vary the amount of current flowing through resistance-heating element 49 to thereby control the length of the pumping cycle. More specifically, if a greater resistance is placed in series with element 49, the timing of the pump will be slowed to provide longer cycles of operation and vice versa. Also, if desired, a variable resistance 91 may be inserted in line 51 for controlling the temperature to which filament 22 heats up. In this respect, less resistance will result in heating filament 22 to a higher temperature and hence there will be a more complete expansion of air in chamber 21 with the development of a greater suction pressure. Conversely, if greater resistance is applied through variable resistance 91, there will be heating of filament 22 to a lower temperature and thus a lower suction pressure. However, in order to prevent the pump's exceeding a predetermined maximum suction pressure which may be injurious to the patient, a valve arrangement such as shown in FIG. 2 may be utilized to limit the maximum suction pressure of the pump. In this respect only housing 61 and its associated structure need be utilized in the suction line to limit the higher pressure, while the various variable resistances and 91 are used to obtain a lower range of suctions.

It can thus be seen that the control valve assembly of the present invention maintains the suction pressure in the suction conduit substantially constant by metering various amounts of air into the suction conduit, as required, while the suction pressure produced by the pump tends to exceed the predetermined suction pressure for which the control valve assembly is set. The amount of atmospheric air which is metered into the suction conduit depends on the spacing between the diaphragm and the valve seat with which it cooperates.

I claim:

1. A medical suction pump for providing a substantially constant suction pressure and a displacement volume which is relatively constant irrespective of variations in external conditions to which said pump may be subjected comprising a pump housing, a chamber in said housing, heating filament means associated with said chamber, electrical circuit means coupled to said heating filament means for periodically passing an electric current through said heating filament means to heat gases in said chamber to provide an exhaust cycle by causing said gases to expand and to provide a suction cycle when said gases cool when said filament means are not being heated, a suction conduit in communication with said chamber, check valve means associated with said chamber and said suction conduit for terminating communication between said suction conduit and said chamber during said exhaust cycle while permitting said gases to be exhausted from said chamber and for permitting communication between said suction conduit and said chamber during said suction cycle, said electrical circuit having a parameter which causes said filament means to be heated to a sufiicient degree to cause said pump to primarily provide a suction pressure which is in excess of a predeten'nined desired pressure, and control valve means for selectively bleeding a variable amount of atmospheric air into said chamber so as to maintain said suction pressure substantially at said desired predetermined value, whereby said suction pump will operate at a substantially constant suction pressure during the major portion of the suction cycle and said displacement volume will remain relatively constant insofar as it is dependent on said suction pressure, said control valve means comprising a valve housing, a diaphragm in said valve housing defining a pressure sensing chamber with said valve housing, a valve seat in said housing, first conduit means for effecting communication between said suction conduit and said pressure sensing chamber, means associated with said diaphragm for effecting a seal relative to said valve seat, second conduit means for effecting communication between said suction conduit and said valve seat, and vent means in said valve housing for permitting atmospheric air to bleed into said second conduit means when said suction pressure in said pressure-sensing chamber exceeds said desired predetermined value.

2. A medical suction pump as set forth in claim 1 including spring means interposed between said housing and said diaphragm for biasing said diaphragm toward said valve seat.

3. A medical suction pump as set forth in claim 2 wherein said means for effecting a seal relative to said valve seat comprises a central portion of said diaphragm on the opposite side therefor from said pressure-sensing chamber.

4. A medical suction pump as set forth in claim 2 including means for adjusting the pressure exerted by said spring on said diaphragm, to thereby selectively vary said predetermined suction pressure.

5. A medical suction pump for providing a substantially constant suction pressure and a displacement volume which is relatively constant irrespective of variations in external conditions to which said pump may be subjected comprising a pump housing, a chamber in said housing, heating filament means associated with said chamber, electrical circuit means coupled to said heating filament means for periodically passing an electric current through said heating filament means to heat gases in said chamber to provide an exhaust cycle by causing said gases to expand and to provide a suction cycle when said gases cool when said filament means are not being heated, a suction conduit in communication with said chamber, check valve means associated with said chamber and said suction conduit for terminating communication between said suction conduit and said chamber during said exhaust cycle while permitting said gases to be exhausted from said chamber and for permitting communication between said suction conduit and said chamber during said suction cycle, said electrical circuit having a parameter which causes said filament means to be heated to a sufficient degree to cause said pump to primarily provide a suction pressure which is in excess of a predetermined desired pressure, and control valve means for selectively bleeding a variable amount of atmospheric air into said chamber so as to maintain said suction pressure substantially at said desired predetermined value, whereby said suction pump will operate at a substantially constant suction pressure during the major portion of the suction cycle and said displacement volume will remain relatively constant insofar as it is dependent on said suction pressure, said control valve means including first and second valve housings, a first diaphragm in said first housing defining a first pressure sensing chamber therewith, a second diaphragm in said second housing defining a second pressure-sensing chamber therewith, first conduit means for effecting pump for providing a substantially constant suction pressure and a displacement volume which is relatively constant irrespective of variations in external conditions to which said pump communication between said suction conduit and said first and second pressure-sensing chambers, a first valve seat in said first valve housing, a second valve seat in said second valve housing, first means for effecting a seal relative to said first seat, second means for effecting a seal relative to said second valve seat, second conduit means for effecting communication between said suction conduit and said first and second valve seats, first relatively strong biasing means for biasing said first diaphragm toward said first valve seat, second relatively weak biasing means for biasing said second diaphragm toward said second valve seat, first vent means in said first housing, second vent means in said second housing, valve means in said second vent means for selectively permitting communication between the atmosphere and said second valve seat, whereby said first means will be unseated from said first valve seat when said suction pressure exceeds a first predetermined relatively high value to permit atmospheric air to bleed into said second conduit means through said first vent means when the suction pressure in said first sensing chamber exceeds a first relatively high value to thereby maintain said suction pressure at said first predetermined relatively high value while said valve means in a closed condition prevent atmospheric air from bleeding through said second vent means, and whereby said second means will unseat from said second valve seat when said valve means permit said second vent means to communicate with the atmosphere to permit atmospheric air to bleed into said second conduit means as a result of the suction pressure in said second pressure-sensing chamber exceeding a second relatively low predetermined value to thereby maintain said suction pressure at said second relatively low predetermined value while said relatively strong biasing means prevents venting through said first vent means.

6. A medical suction pump as set forth in claim 5 wherein said first and second means for effecting a seal relative to said first and second valve seats, respectively. comprise central portions of said first and second diaphragms, respectively.

7. A medical suction pump for producing a substantially constant predetermined suction pressure comprising pump means for primarily producing a suction pressure in excess of said predetermined suction pressure, control valve means coupled to said pump means and responsive to said suction pressure produced by said pump means for venting a sufficient amount of atmospheric air into said pump means to maintain said substantially constant predetermined suction pressure, a suction conduit coupled to said pump means, said control valve means being in communication with said suction conduit for causing the suction pressure in said conduit to be maintained at said substantially constant predetermined value while the suction pressure produced by said pump means is in excess of said predetermined value, said control valve means including a housing, a diaphragm in said housing defining a pressure-sensing chamber with said housing, said suction conduit being in communication with said chamber, a seat in said housing, means on said diaphragm for effecting a seal with said seat, and a vent in said housing placed in communication with said suction conduit when said diaphragm is moved out of contact with said seat by suction pressure in said chamber, thereby to reduce the suction pressure in said suction conduit to produce said substantially constant predetermined suction pressure.

8. A medical suction pump as set forth in claim 7 including spring means interposed between said housing and said diaphragm for biasing said diaphragm toward said valve seat.

9. A medical suction pump as set forth in claim 8 including means for adjusting the pressure exerted by said spring on said diaphragm, to thereby selectively vary said predetermined suction pressure.

10. A medical suction pump as set forth in claim 8 wherein said means associated with said diaphragm for effecting a seal relative to said valve seat comprises a central portion of said diaphragm on the opposite side thereof from said pressuresensing chamber.

11. A medical suction pump for producing a substantially constant predetermined suction pressure comprising pump means for primarily producing a suction pressure in excess of said predetermined suction pressure, control valve means coupled to said pump means and responsive to said suction pressure produced by said pump means for venting a sufficient amount of atmospheric air into said pump means to maintain said substantially constant predetermined suction pressure, a suction conduit coupled to said pump means, said control valve means being in communication with said suction conduit for causing the suction pressure in said conduit to be maintained at said substantially constant predetermined value while the suction pressure produced by said pump means is in excess of said predetermined value, said control valve means comprising a valve housing, a diaphragm in said valve housing defining a pressure sensing chamber with said valve housing, a valve seat in said housing, first conduit means for effecting communication between said suction conduit and said pressure sensing chamber, means associated with said diaphragm for effecting a seal relative to said valve seat, second conduit means for effecting communication between said suction conduit and said valve seat, and vent means in said valve housing for pennitting atmospheric air to bleed into said second conduit means when said suction pressure in said pressure-sensing chamber exceeds said desired predetermined value so as to cause said diaphragm to be unseated from said valve seat.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 1 Dated November 30, Inventor) Stanford A. Henderson and that said Letters Patent are ppears in the above-identified patent It is certified that error a hereby corrected as shown below:

' In the Abstract, line 11, before "predetermined" insert Column 5, line 58, change "61" to -83; line 59, change "83 to -6l'-.

Column 7, lines 38-41 (claim 5) cancel "pump for providing a substantially constant suction pressure and a displacement volume which is relatively constant irrespective of variations in external conditions to which said pump".

Signed m] sea led 51115;; 16 th day of May 1972 (SE/1L) A; 0: st:

KII A'JKRD I LFLJCTCBFIE JR E0 BERT G-OTTSCf-MLK Atuestim; Oifi C(fl" 

1. A medical suction pump for providing a substantially constant suction pressure and a displacement volume which is relatively constant irrespective of variations in external conditions to which said pump may be subjected comprising a pump housing, a chamber in said housing, heating filament means associated with said chamber, electrical circuit means coupled to said heating filament means for periodically passing an electric current through said heating filament means to heat gases in said chamber to provide an exhaust cycle by causing said gases to expand and to provide a suction cycle when said gases cool when said filament means are not being heated, a suction conduit in communication with said chamber, check valve means associated with said chamber and said suction conduit for terminating communication between said suction conduit and said chamber during said exhaust cycle while permitting said gases to be exhausted from said chamber and for permitting communication between said suction conduit and said chamber during said suction cycle, said electrical circuit having a parameter which causes said filament means to be heated to a sufficient degree to cause said pump to primarily provide a suction pressure which is in excess of a predetermined desired pressure, and control valve means for selectively bleeding a variable amount of atmospheric air into said chamber so as to maintain said suction pressure substantially at said desired predetermined value, whereby said suction pump will operate at a substantially constant suction pressure during the major portion of the suction cycle and said displacement volume will remain relatively constant insofar as it is dependent on said suction pressure, said control valve means comprising a valve housing, a diaphragm in said valve housing defining a pressure sensing chamber with said valve housing, a valve seat in said housing, first conduit means for effecting communication between said suction conduit and said pressure sensing chamber, means associated with said diaphragm for effecting a seal relative to said valve seat, second conduit means for effecting communication between said suction conduit and said valve seat, and vent means in said valve housing for permitting atmospheric air to bleed into said second conduit means when said suction pressure in said pressure-sensing chamber exceeds said desired predetermined value.
 2. A medical suction pump as set forth in claim 1 including spring means interposed between said housing and said diaphragm for biasing said diaphragm toward said valve seat.
 3. A medical suction pump as set forth in claim 2 wherein said means for effecting a seal relative to said valve seat comprises a central portion of said diaphragm on the opposite side thereof from said pressure-sensing chamber.
 4. A medical suction pump as set forth in claim 2 including means for adjusting the pressure exerted by said spring on said diaphragm, to thereby selectively vary said predetermined suction pressure.
 5. A medical suction pump for providing a substantially constant suction pressure and a displacement volume which is relatively constant irrespective of variations in external conditions to which said pump may be subjected comprising a pump housing, a chamber in said housing, heating filament means associated with said chamber, electrical circuit means coupled to said heating filament means for periodically passing an electric current through said heating filament means to heat gases in said chamber to provide an exhaust cycle by causing said gases to expand and to provide a suction cycle when said gases cool when said filament means are not being heated, a suction coNduit in communication with said chamber, check valve means associated with said chamber and said suction conduit for terminating communication between said suction conduit and said chamber during said exhaust cycle while permitting said gases to be exhausted from said chamber and for permitting communication between said suction conduit and said chamber during said suction cycle, said electrical circuit having a parameter which causes said filament means to be heated to a sufficient degree to cause said pump to primarily provide a suction pressure which is in excess of a predetermined desired pressure, and control valve means for selectively bleeding a variable amount of atmospheric air into said chamber so as to maintain said suction pressure substantially at said desired predetermined value, whereby said suction pump will operate at a substantially constant suction pressure during the major portion of the suction cycle and said displacement volume will remain relatively constant insofar as it is dependent on said suction pressure, said control valve means including first and second valve housings, a first diaphragm in said first housing defining a first pressure sensing chamber therewith, a second diaphragm in said second housing defining a second pressure-sensing chamber therewith, first conduit means for effecting communication between said suction conduit and said first and second pressure-sensing chambers, a first valve seat in said first valve housing, a second valve seat in said second valve housing, first means for effecting a seal relative to said first seat, second means for effecting a seal relative to said second valve seat, second conduit means for effecting communication between said suction conduit and said first and second valve seats, first relatively strong biasing means for biasing said first diaphragm toward said first valve seat, second relatively weak biasing means for biasing said second diaphragm toward said second valve seat, first vent means in said first housing, second vent means in said second housing, valve means in said second vent means for selectively permitting communication between the atmosphere and said second valve seat, whereby said first means will be unseated from said first valve seat when said suction pressure exceeds a first predetermined relatively high value to permit atmospheric air to bleed into said second conduit means through said first vent means when the suction pressure in said first sensing chamber exceeds a first relatively high value to thereby maintain said suction pressure at said first predetermined relatively high value while said valve means in a closed condition prevent atmospheric air from bleeding through said second vent means, and whereby said second means will unseat from said second valve seat when said valve means permit said second vent means to communicate with the atmosphere to permit atmospheric air to bleed into said second conduit means as a result of the suction pressure in said second pressure-sensing chamber exceeding a second relatively low predetermined value to thereby maintain said suction pressure at said second relatively low predetermined value while said relatively strong biasing means prevents venting through said first vent means.
 6. A medical suction pump as set forth in claim 5 wherein said first and second means for effecting a seal relative to said first and second valve seats, respectively, comprise central portions of said first and second diaphragms, respectively.
 7. A medical suction pump for producing a substantially constant predetermined suction pressure comprising pump means for primarily producing a suction pressure in excess of said predetermined suction pressure, control valve means coupled to said pump means and responsive to said suction pressure produced by said pump means for venting a sufficient amount of atmospheric air into said pump means to maintain said substantially constant predetermined suction pressure, a suction conduit coupled to said pump means, sAid control valve means being in communication with said suction conduit for causing the suction pressure in said conduit to be maintained at said substantially constant predetermined value while the suction pressure produced by said pump means is in excess of said predetermined value, said control valve means including a housing, a diaphragm in said housing defining a pressure-sensing chamber with said housing, said suction conduit being in communication with said chamber, a seat in said housing, means on said diaphragm for effecting a seal with said seat, and a vent in said housing placed in communication with said suction conduit when said diaphragm is moved out of contact with said seat by suction pressure in said chamber, thereby to reduce the suction pressure in said suction conduit to produce said substantially constant predetermined suction pressure.
 8. A medical suction pump as set forth in claim 7 including spring means interposed between said housing and said diaphragm for biasing said diaphragm toward said valve seat.
 9. A medical suction pump as set forth in claim 8 including means for adjusting the pressure exerted by said spring on said diaphragm, to thereby selectively vary said predetermined suction pressure.
 10. A medical suction pump as set forth in claim 8 wherein said means associated with said diaphragm for effecting a seal relative to said valve seat comprises a central portion of said diaphragm on the opposite side thereof from said pressure-sensing chamber.
 11. A medical suction pump for producing a substantially constant predetermined suction pressure comprising pump means for primarily producing a suction pressure in excess of said predetermined suction pressure, control valve means coupled to said pump means and responsive to said suction pressure produced by said pump means for venting a sufficient amount of atmospheric air into said pump means to maintain said substantially constant predetermined suction pressure, a suction conduit coupled to said pump means, said control valve means being in communication with said suction conduit for causing the suction pressure in said conduit to be maintained at said substantially constant predetermined value while the suction pressure produced by said pump means is in excess of said predetermined value, said control valve means comprising a valve housing, a diaphragm in said valve housing defining a pressure sensing chamber with said valve housing, a valve seat in said housing, first conduit means for effecting communication between said suction conduit and said pressure sensing chamber, means associated with said diaphragm for effecting a seal relative to said valve seat, second conduit means for effecting communication between said suction conduit and said valve seat, and vent means in said valve housing for permitting atmospheric air to bleed into said second conduit means when said suction pressure in said pressure-sensing chamber exceeds said desired predetermined value so as to cause said diaphragm to be unseated from said valve seat. 